Electrical braking systems of the type having electromagnetically actuated brakes on a trailing vehicle controlled by a cylindrically wound resistor having a yieldable contact member which rolls over the coils of the resistor have been known for over twenty years. Such systems are relatively inexpensive, and have been made in sizable quantities; but the service life of such units has not increased appreciably over the years. A build up of dirt and corrosion of the coils and contact strip causes the electrical output of the unit to decrease with service. Another problem that has existed with such units is that the geometry of the yieldable contact member across the wound resistor inherently produces an electrical output that is not a replica of the force applied by the operator. Another problem that has existed with such units is that irregularities of the core of the wound resistor causes nonuniform contact pressure of the rolling contact to in turn cause arcing with some of the windings thereby further shortening the life of the unit.
An object of the present invention, therefore, is the provision of a new and improved helically wound electrical control unit for electromagnetically actuated brake systems and the like, which will produce a positive incrementally increasing output as the contact strip rolls across the windings and so that contact is assured with specific predetermined ones of the winding.
Another object of the present invention is the provision of a new and improved unit of the above described type in which arcing is reduced between the contact and the windings of the resistor.
Another object of the present invention is the provision of a new and improved unit of the above described type whose electrical output is predetermined by plateaus and depressions on the surface of the insulator member over which the resistance wire is wound, so that the electrical output of the unit can be positively adjusted by changing the spacing between the plateaus.
A still further object of the present invention is the provision of a new and improved braking system of the above described type wherein a bright light will appear on initial actuation if an open circuit exists to the towed vehicle. If, on the other hand, a proper connection to the trailer brakes exists, the light will be turned on in incremental stages as the electrical output of the controller increases.
Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments described with reference to the accompanying drawings forming a part of this specification.